Spraying wheat with plant growth regulators during the crop’s reproductive stage was associated with higher yields and more above-ground biomass in a two-season field trial conducted under natural heat stress after flowering. In 2024, grain yields were 30.21% to 33.19% higher than in untreated plots across the four spray programs tested. In 2025, the mixed treatment increased yield by 9.42%.
The treatments also increased leaf area and several measures of photosynthetic activity, the process by which leaves use light to build plant matter. But the results were not identical from one season to the next, and the experiment covered one wheat cultivar at one field location, so the findings do not yet show how the approach would perform more broadly.
A clearer difference in the first season
The trial compared untreated wheat with four foliar treatments: epibrassinolide, melatonin, potassium phosphate, and a mixture containing lower doses of all three. In 2024, the treatments did not significantly change the number of spikes, but they did raise the number of grains per spike by 24.43% to 32.43%. Epibrassinolide and melatonin also increased the weight of 1,000 grains by 2.87% and 4.07%, respectively.
The gains in total above-ground dry matter were more consistent. Compared with untreated plants, the four treatments increased dry matter by 11.61% to 13.95% in 2024 and by 5.60% to 11.43% in 2025. The mixture produced the largest reported increase in both seasons.
Leaf measurements pointed to one possible reason for the extra biomass. In 2024, flag-leaf area rose by 25.71% to 51.14%, depending on the treatment, while total leaf area rose by 23.39% to 45.32%. The mixture increased flag-leaf area by 26.75% in 2025.
Leaves stayed active under heat
Several gas-exchange measurements also improved in 2024. The rate at which leaves took in carbon dioxide for photosynthesis rose by 5.08% to 12.44% under the treatments with reported increases. Epibrassinolide and the mixture also raised measures linked to the opening of leaf pores, internal carbon dioxide concentration and water loss from leaves.
Those effects were less uniform in 2025. All regulator treatments increased total leaf area, but the reported results did not show a significant difference from untreated wheat for transpiration, the movement of water vapour from leaves. That seasonal variation matters because it suggests the sprays did not produce one fixed response under every set of field conditions.
How the field trial was run
Researchers tested semi-winter wheat cultivar ‘Luyan 951’ during the 2024 and 2025 growing seasons in Huantai County, Zibo City, in China’s Shandong province. The randomized complete block trial had five treatment groups and three biological replicates per treatment. Foliar spraying was carried out twice, at booting and flowering.
The control plots received distilled water. The other plots received 0.1 micromoles per litre of epibrassinolide, 100 micromoles per litre of melatonin, 30 millimoles per litre of potassium phosphate, or a mixture containing 0.05 micromoles per litre of epibrassinolide, 50 micromoles per litre of melatonin and 15 millimoles per litre of potassium phosphate.
The study set out to test whether foliar epibrassinolide and melatonin could trigger changes in heat-responsive genes and improve the crop’s tolerance to heat. At maturity, the researchers measured grain yield, grains per spike and 1,000-grain weight. They also dried representative leaves, stems and spikes to measure dry matter. On the 20th day after flowering, they assessed flag-leaf area, leaf greenness and four gas-exchange measures, alongside indicators of reactive oxygen damage and antioxidant activity.
What the results can, and cannot, establish
The researchers interpret the results as showing that the sprays coordinated photosynthetic maintenance, antioxidant defense and related gene activity, helping wheat retain biomass and yield during heat stress. For gene-expression analysis, they used DESeq2 and counted genes as differentially expressed only when the false discovery rate was no greater than 0.05 and the absolute fold change was at least two. The transcriptomic comparison focused on epibrassinolide and melatonin at one post-anthesis time point.
The study does not establish that the observed gene-expression changes caused the yield response, or that the mixture is the best option across cultivars, locations or seasons. Three biological replicates were used for each treatment, and the supplied analysis does not include confidence intervals, absolute yield values or complete numerical results for every comparison. Further trials would be needed to separate the effects of the three mixture components and test whether the pattern holds under other field conditions.
Paper data and sources
Original title: Exogenous plant growth regulators alleviate natural high temperature stress after anthesis in wheat (Triticum aestivum L.) by sustaining efficient photosynthesis and antioxidant defense responses
Authors: Ju F, Zhao F, Gao C et al.
Journal/Repository: Frontiers in plant science
Status: Peer-reviewed
First online: 2026-10-10
DOI: Not available
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